1. Field of the Invention
This invention relates generally to antenna assemblies and more particularly to a new and improved dual slot antenna assembly.
2. Description of the Prior Art
The use of antenna assemblies for both transmission and reception of radio signals is well known, and such antenna assemblies have taken many diverse dimensions and/or shapes to accomplish given objectives. Among such antennas known in the art are those useful in conjunction with propelled vehicles including missiles and more particularly missiles which carry instrument payloads for short term measurements of very high altitude environment data, which data is transmitted from an antenna mounted on a missile to receiving stations on the ground, which receiving stations are often ground tracking stations. However, monitoring has been found to be difficult due to signal nulls encountered as the vehicles assume different roll and aspect orientations.
Although the problem has been attacked in many ways, including the use of refined circuitry such as automatic gain control amplifiers which have to some effect alleviated the problem of antenna deficiencies, there still has been a need to improve the antennas so as to develop radiation patterns without signal lobes of varying strength. More particularly, the antenna should be characterized by an isotropic antenna radiation coverage, that is, a pattern of constant relative power for any orientation of the antenna. As such, the pattern coverage is then relatively constant regardless of the roll or aspect orientation of the rocket, thereby facilitating data monitoring at a tracking station. The avoidance of signal nulls as a characteristic of the antenna eliminates an important deficiency that has previously caused temporary loss of signal information, and in the case of an unrecovered rocket, permanent loss thereof.
Although some previous attempts have been made to design antennas having patterns more nearly isotropic for use in rockets carrying environmental data sensors and associated instruments for telemetry purposes and the like, such antennas have not completely solved the problems in all cases due to one or more of such diverse reasons as failing to satisfy strict aerodynamic design requirements, exhibiting intolerable signal variations in the aspect patterns (the signal pattern measured about the missile in a plane containing the missile) and/or in the roll patterns (the signal pattern measured about the missile in a plane perpendicular to the missile axis), requiring complicated and often expensive components due to complex design requirements, and/or requiring excessive time and/or material in assembly so as to make antenna costs too high for at least some intended uses. For example, the aspect and roll radiation patterns in some antennas of recent design have been found to fluctuate as much as 30 db from isotropic radiation, while the required dimensions and/or costs inherent in other such antennas have made these antennas unusable, or at least undesirable, for many intended uses.